Study On Establishment And Diagnosis Of Critical Nitrogen Concentration Dilution Model In Double Cropping Rice

Excess or deficiency of nitrogen significantly affect on the growth,yield and quality of crops.To achieve crop high quality,high yield and efficiency goals,crop nitrogen nutrition diagnosis and precise control have become the core of precision agriculture research.In this study,systematic analysis of shoot biomass,nitrogen concentration and leaf area index were conducted based on the nitrogen experiments for early and late rice in Nanchang,Jiangxi.According to the theory of critical nitrogen concentration the critical nitrogen concentration dilution curve model(Critical nitrogen dilution curve,Nc)based on the dry weight and leaf area index were constricted for early and late rice respettivrly,and the nitrogen nutrition index(Nitrogen nutrition index,NNI)at different stages were calculated.And the NNI was estimated using normalized difference vegetation index(Normalized difference vegetation index,NDVI)at different periods.Meanwhile,the yield estimation models based on the integrated nitrogen nutrition index(Integrated NNI,NNIint)and integrated normalized difference vegetation index(Integrated NDVI,NDVIint)and according to nitrogen balance theory nitrogen topdressing models based on nitrogen nutrition index were established for early and late rice.Results provided technical support and theoretical basis in nitrogen diagnosis and precise management for double cropping rice in south of China.First,through the analysis of plant nitrogen concentration and dry matter dynamic changes over time,using the method of Justes we have constructed the critical nitrogen concentration dilution model(early rice:Nc = 3.37W-0 44;late rice:Nc = 3.69W-0 34)based on dry matter and established the relationship between NNIint and relative yield(RY).After compared with other exiting rice critical nitrogen concentration curves differences were found between the Japonica and Indica model parameters.Integrated NNI and RY had a significant linear relationship at different period and the entire growth period model performance best.After the independent data validation,critical nitrogen concentration dilution model can distinguish the N limiting and non-limiting growth for early and late rice,models can diagnose N status well;yield estimation models based on NNIint at different peroid can be good tools in predicting grain yield.Secondly,based on the critical model based on the dry matter,were constructed early and late rice critical nitrogen concentration model based on leaf area index(early rice:NcEarly=3.25LAI-0.34,late rice:NcLate =3.51LAI-0.31)as well as nitrogen uptake and nitrogen regulation model.The results showed that,LAI and plant nitrogen concentration can fit to the power function well.There were slight differences between the present curves and existing LAI-based curves.Compared with the critical model based on dry matter,we concluded that among the different environments and species LAI-based model performed more stable.Then based on the relationship between NNI and nitrogen accumulation we established a model of N topdressing model with target yield for tillering and panicle initiation period.The model can be applied to the local fertilizer management.Finally,NNI estimation model and yield prediction model was constructed based on NDVI.The results showed that,NDVI values increased with increasing nitrogen levels;at the same period,NDVI under different N treatments had significant differences;different periods relationship between NDVI and NNI and integrated NDVI and RY showed a significant positive correlation.NNI values were estimated best by NDVI at jointing stage,the model were,early rice:NBNI = 0.4309e1.37l14NDVI;late rice:NNI = 0.0753e3 4709NDVI.The yield estimation models at different growth stages were stable,howerver,there are significant differences between early and late rice.